The thymus has been recognized as an endocrine gland having a major function in the immunological defense system of the body. Recently, crude extracts of calf thymus have been shown to contain a family of hormones, referred to as thymosins, having molecular weights ranging from approximately 3,200 to 70,000 daltons. See for example, Trainin, N., Physiological Reviews, Vol. 54, p. 272 (1974) and White, A., Ann. N.Y. Acad. Sci., Vol. 29, p. 253 (1975).
These hormones are believed to act by regulating the rate of maturation of incompentent, as yet unidentified, precursor cells to competent lymphocytes (T-cells) and thus to become effective fighters against foreign invaders. In addition, precursor cells of other types, e.g., erythroid, are stimulated in their production and maturation by thymosin preparations. Recently, a relatively crude calf thymus extract containing thymosin was used to increase the immunologic competence of a young girl born with impaired immunity. Wara, D.W., et al., New Eng. J. Med., Vol. 292, p. 70 (1975). Also a recent report has described improvement in the total hematological status (increase in number of both white and red cells) in patients treated with a thymosin preparation. See Alexsandrowicz, J., et al., Proc. Intl. Congress Immunol., Brighton, England, July 22-24, 1974.
There have also been reports, see for example Bach, J. F., et al., Immunology, Vol. 25, p. 353 (1973), that thymosin-like activity has been detected in fresh pig blood. The factor responsible therefor is believed to have a molecular weight of approximately 1,000 daltons.